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  • 1
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electrospray mass spectra of a series of substituted 2-nitrobenzene diazonium cations reveal a surprising stability of the intact ion to the collisionally activated loss of nitrogen, contrary to the behaviour of monosubstituted benzenediazonium ions reported previously. Ions bearing elecron-releasing groups at the para position, e.g. 4-CH3, 4-CH3O, and 4-C6H5O, all experience loss of this para substituent rather than loss of nitrogen. However, ions bearing electron-withdrawing para substituents, e.g. 4-NO2 4-CN, 4-CF3 and 4-Cl, all undergo nuleophilic displacement of the 2-nitro group by water to give the corresponding phenol derivative, which subsequently loses nitrogen. The exceptional stability of these substituted 2-nitrobenzene diazonium salts is attributed to a favourable coulombic interaction between the positive charge on the diazonium group and the partial negative charge on one of the oxygen atoms of the nearby nitro group. Once that nitro group has been removed, the resulting substituted 2-hydroxybenzenediazonium cation loses nitrogen in the normal way.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1433-0768
    Keywords: Key words Iodopentacarbonyl chromium(0) [Cr(CO)5I] ; Electrochemical quartz crystal microbalance (ECQCM) ; Ion transfer ; Voltammetry ; Mechanically attached solid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electrochemistry of microcrystals of [(C4H9)4N][Cr(CO)5I] attached to a gold electrode which is placed in aqueous (lithium or tetrabutylammonium perchlorate) electrolyte media has been studied in detail by chronoamperometric, voltammetric and electrochemical quartz crystal microbalance (ECQCM) techniques. Whilst chronoamperometric and voltammetric measurements show that the expected one-electron oxidation of microcrystalline [Cr(CO)5I]− solid to Cr(CO)5I occurs at the solid-electrode-solvent (electrolyte) interface, the ECQCM measurements reveal that charge neutralization does not occur exclusively via the expected ejection of the tetrabutylammonium cation. Rather, uptake of ClO4 − occurs under conditions where the solubility of sparingly soluble [(C4H9)4N]ClO4 is exceeded. This is the first time that uptake of an anion rather than loss of a cation has been detected in association with an oxidation during electrochemical studies of microcrystals attached to electrode surfaces. It is therefore now emerging that analogous charge neutralization processes to those encounted in voltammetric studies on conducting polymers are available in voltammetric studies of microcrystals attached to electrodes which are placed in contact with solvent (electrolyte) media. In the presence of LiClO4 as the electrolyte, an ion exchange process occurs leading to formation of Li[Cr(CO)5I] . X H2O which then slowly dissolves in water at a rate that is strongly influenced by the electrolyte concentration, the relatively hydrophobic nature of the [(C4H9)4N]+ cation and the poor solubility of [(C4H9)4N]ClO4.
    Type of Medium: Electronic Resource
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